The disclosed embodiments relate to data transmission in wireless communications systems.
Data transmissions include telephony data and other data, such as control data. In typical wireless telecommunications environments, it is important to provide security for the telephony data transmitted on a radio frequency (“RF”) channel between a wireless network subscriber's mobile unit and a fixed base. Secure communication allows users to be confident their communications are private and guarded from fraud.
Various techniques for securing telephony data transmitted over the RF channel include encrypting the telephony data for transmission over the RF channel. The telephony data is decrypted when received. Encryption techniques often employ a mathematical algorithm that alters or rearranges the telephony data using a key. A corresponding key must be used to decrypt the telephony data. Keys are usually changed periodically for security. One challenge for designers of such techniques is the need to synchronize the encryption mechanisms for equipment and/or software at the sending and receiving locations. Synchronization includes assuring that the sender and the receiver are using a current key, and the sender and receiver are encrypting and decrypting at an appropriate point in a transmission.
Synchronization must be established initially and maintained, even through situations in a wireless environment such as signal fading and handoff of an ongoing telephony call from one base station to another. Encryption synchronization in a wireless communication system can be difficult because the base station and remote unit are physically separated, and also because telephony calls (including low-speed modem calls and facsimile calls) are relatively asynchronous (e.g., no connection without an active call).
Prior approaches to encryption and synchronization have various disadvantages such as added signal processing overhead and time. For example, one technique used with a secure radiotelephone requires an additional infrared (“IR”) link to establish and maintain encryption synchronization. Another method involving analog scrambling of the telephony data uses an additional sub-audible signal for continuous synchronization of the scrambled audio signal. One method for resynchronization of the encryption system after a handoff requires a processing delay that is in addition to any normal handoff delay
Overall, there is a need for synchronization of encryption that avoids the above disadvantages while providing secure wireless communication.
In the drawings, the same reference numbers identify identical or substantially similar elements or acts. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced (e.g., element 204 is first introduced and discussed with respect to FIG. 2).
Note: the headings provided herein are for convenience and do not necessarily affect the scope or interpretation of the invention.